In the clinical chemistry laboratory art, it is well known that certain blood tests and assays require certain preservatives to be used if those tests are to be performed reliably. The main reason is that blood tends to coagulate rather quickly and certain blood test reagents require that the blood sample be in a fluid state to permit mixing. Another reason is that the fluidic systems on which several blood analyzers are built require that the blood remains in a fluid state so that blockages of conduits and chambers are avoided and the sample can be effectively washed from the testing chamber after the test is complete. Several anticoagulation reagents are available and these inhibit in various well known ways, the natural coagulation process. For example, calcium ions are required as part of the coagulation cascade, so by adding excess ethylenediaminetetra acetic acid (EDTA) to the blood sample at the time of collection, the calcium ions can be sequestered, by coordination with the EDTA, and coagulation prevented. As is well known in the clinical chemistry art, only certain anticoagulants are suitable for certain blood tests.
From a clinical perspective, when a user (e.g. nurse, physician, phlebotomist), decides a certain blood test or set of blood tests is required, the user then selects the appropriate collection device. This is typically a coated capillary tube, if the sample is to be taken using a fingerstick, e.g. by means of a lancet. More typically, venipunture is used, where a needle is inserted into a vein and the other end of the needle is mated with an evacuated collection tube. This is generally done using a Vacutainer® which is an evacuated tube with a colored stopper. The evacuated tube also contains a blood sample stabilizing reagent or preservative, which can be a heparin salt, a chelating agent such as EDTA, or some other anticoagulant material. The color of the stopper is generally used as a simple means to identify the anticoagulant reagent in the tube, e.g. green stopper for heparin, purple for EDTA, and so on. While users are generally experienced in selecting the correct tube for a given test set, there is still the opportunity for error in tube selection. This is because the user, typically a nurse, is busy and has many other tasks to complete and can be interrupted during any given task. For background on Vacutainer® see: http://en.wikipedia.org/wiki/Vacutainer. Some facilities actually restrict themselves to one collection tube manufacturer in the interest of eliminating errors.
A widely used indirect strategy in the laboratory testing art that can catch such errors in collection tube selection, is to place a reportable range on a given blood test, and if an individual sample analysis is outside of the reportable range, then an algorithm within the analyzer flags or otherwise identifies the test result as unreportable or out of range. However, there are many reasons why an analysis system may flag a given test result as being unreportable that are not based on incorrect sample collection. These include the possibility that the sensor or detection means is not operating to specification due, for example, to one or more of the following; an incomplete wash cycle, temperature fluctuation outside a preset range, calibration malfunction and expired reagent. Those skilled in the art that will recognize that these are but a few of the potential reasons. Among them of course is the possibility that the sample was collected using the wrong anticoagulant. However, prior art systems do not provide a means for isolating the latter reason as the specific cause and explicitly identifying this cause to the user.
By way of confirmation of the state of the art, in experiments showing that when an EDTA sample was intentionally run on prior art electrolyte analyzing instruments, e.g. i-STAT® and a radiometer, only the potassium and calcium results are suppressed, as would be expected as these values should be out of range. None of the other tests provided by the prior art instruments, e.g. pO2, pH, pCO2 and lactate were flagged as being abnormal and there was no indication by the instrument that the wrong type of collection device had been used.
Because the answer from these analyzers are often used to make a clinical decision that can significantly impact the health and well-being of a patient, there remains a need for blood analysis systems to integrate an ability to distinguish the specific cause of a failed blood analysis, notably where the cause is the use of an incorrect sample collection method. Furthermore, subtle effects that are less pronounced on sensor performance and are not typically recognized as being caused by incorrect anticoagulation, need to be identified. The present invention seeks to ameliorate these deficiencies in the prior art and also provide automatic means for alerting users to incorrect sample collection for given test sets.